1. Field of the Invention
The present invention relates to sensor systems and, more specifically, to a nanoscale substance sensor.
2. Description of the Prior Art
Substance sensors are used in a wide variety of applications, including medical diagnostics, contraband detection, chemical process metrology, hazardous substance detection and any process where the detection or measurement of a substance is necessary. Many different bulk substance detection and measuring tests are well known to those of skill in the chemical and biomedical arts. Such tests usually involve reaction of the target substance with a test material to induce a change is a physical property of the test material. For example, litmus paper is a well known test material for detecting the presence of acids.
In some applications, the target substance is present in extremely low concentrations and is, therefore, hard to detect using conventional bulk chemical testing systems. For example, detecting contraband (e.g., explosives and illegal narcotics) can be difficult in real time using conventional chemical testing. Detection systems for these types of substances often fail to detect a substance when it is present below a certain concentration, even though a dangerous amount may be present.
Certain animals, such as dogs, can be trained to detect a target substance by smelling it in the air. However, animals often give false positive results and false negative results. They also sometimes cannot detect a target substance when it is masked by another substance. Also, the training and maintenance of such animals is quite costly.
Recently, functionalized cantilever sensors have been developed to detect target substances. Such sensors employ a cantilever that has been functionalized on one side with a material that reacts to a target substance. When the material is exposed to the target substance in sufficient quantity, the material will induce surface stress on the cantilever, thereby causing it to deform. The deformation may be detected in one of several manners, including using an optical displacement sensor. Such cantilevers typically have a width in the tens of micrometers. While micro-scale cantilevers can provide real time data, their micro-scale width limits their sensitivity.
Currently, most cantilever sensors are made with micro-electro-mechanical systems (MEMS) mask and etching processes. A typical size of the cantilever is approximately tens of micrometers in width. This relatively large size of MEMS cantilevers limits the sensitivity of these sensors because the ratio of functionalized area to displacement is limited. Reducing the size of the cantilever would improve sensitivity, but existing displacement sensing systems become increasingly imprecise as the cantilever size is reduced.
Therefore, there is a need for a sensor system that can detect extremely low concentrations of target substances in real time with a high level of precision.